When an optical multiplexer/demultiplexer having an optical waveguide is connected with optical fibers, precisely aligning the optical axis of the optical waveguide with the optical axis of the optical fibers is essential to reduction of optical transmission loss at the connection site.
Accordingly, techniques for aligning the optical axis of an optical waveguide with the optical axis of an optical fiber have been proposed in the past.
For example, there has been a proposal for an optical device in which an optical axis aligning guide and an optical waveguide are formed simultaneously by performing photolithography on a photosensitive resin on a support (see Japanese Laid-Open Patent Publications H1-316710 and H2-62502).
The optical axis aligning guide is provided in order to precisely align the optical axis of an optical waveguide with the optical axis of an optical fiber which is connected with the end face of the optical waveguide. The shape of the optical axis aligning guide is determined by the shape of the optical fiber.
A methacrylate resin capable of transmitting light having a wavelength of 0.66 μm, and the like, can be used as the photosensitive resin which is the material of the optical axis aligning guide.
The light having a wavelength of 0.66 μm that is mentioned in the above-described publications is transmitted by a multi-mode optical fiber.
Meanwhile, another type of optical fiber besides a multi-mode optical fiber is a single-mode optical fiber for transmitting single-mode light having a wavelength of 1.31 or 1.55 μm, which is used in general trunk systems.
This single-mode optical fiber has a small core having a diameter of approximately 10 μm, which means that the diameter is only about ⅕ and the cross sectional area is only about 1/25 compared with those of the core of a multi-mode optical fiber, so there is a need for a single-mode optical device with which optical axes can be aligned at high precision.
The following problems are encountered when the techniques discussed in the above-described publications are applied to a single-mode optical device.
(1) When a (meth)acrylate radiation-sensitive resin is used as the material to produce a single-mode optical component by photolithography, it is difficult to precisely align the optical axis of the optical waveguide of the single-mode optical component with the optical axis of a single-mode optical fiber having a small diameter.
(2) When a (meth)acrylate radiation-sensitive resin is used, because of the large amount of light absorption at a wavelength of 1.31 or 1.55 μm, a practical level of transmission efficiency cannot be attained.
(3) The heat resistance is not high enough to meet the requirement for improving the reliability of an optical device.
To solve problem (1) in particular, it is necessary to use an alkali developing method which involves the use of a basic substance-containing solution such as an alkaline aqueous solution, instead of a developing method which involves the use of an organic solvent, so as to increase the resolution by photolithography. However, when a (meth)acrylate radiation-sensitive resin is used together with an alkaline aqueous solution, the acid component required in the resin for alkali developing exhibits light absorption at the usage wavelengths (1.31 μm, 1.55 μm) of single-mode light, resulting in a problem of a decrease of optical transmission efficiency.